A hybrid vehicle may include an engine and a motor for propelling the hybrid vehicle. The engine may operate at various speeds and loads to provide a desired driver demand torque while the hybrid vehicle is operating. The engine's brake specific fuel consumption may vary significantly between different operating conditions. The changes in fuel consumption may be related to engine pumping losses, engine friction, accessory losses, knock limits, and other conditions. Consequently, it may be desirable to operate the engine at one condition to conserve fuel; however, the hybrid driveline may not be able to provide driver demand torque over a desired driveline operating range when engine torque is confined to efficient engine operating conditions. Therefore, the hybrid driveline may be operated at conditions where the engine is less efficient than is desired to meet driver demand over a wide range of vehicle speeds.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method, comprising: defining an efficient engine operating region over an engine operating domain; applying a first filter to a desired engine power if the desired engine power is within the efficient engine operating region; applying a second filter to the desired engine power if the desired engine power is not within the efficient engine operating region; and commanding an engine to operate at a filtered engine power.
By applying different filters to desired engine power, it may be possible to retain engine operation within a range where engine efficiency is greater for a longer period of time, thereby improving hybrid driveline efficiency. In particular, if desired engine power is within a defined efficient engine operating range, desired engine power may be more heavily filtered so that if desired engine power exits the defined efficient engine operating range, filtered engine power may remain in the defined efficient engine operating range. The engine may be operated at the filtered engine power to increase driveline efficiency. A motor/generator may provide a difference in power between the desired engine power and the filtered engine power so that driver demand torque may be provided. On the other hand, if desired engine power is outside of the defined efficient engine operating range, the filtered engine power may be less heavily filtered so that if desired engine power enters the defined efficient engine operating range, filtered engine power may enter the defined efficient engine operating range sooner than if desired engine power were filtered as if desired engine power was in the defined efficient engine operating range.
The present description may provide several advantages. In particular, the approach may improve vehicle efficiency. Additionally, the approach may provide fewer transitions between engine operating conditions. Further, the approach may provide lower vehicle emissions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.